Several known functional MR imaging studies based on detection of temporary changes in T2* which result from local changes in magnetic susceptibility have been conducted. Among these are measurements of regional cerebral blood volume (rCBV) using a bolus injection of contrast agent (A. Villringer et al, Magn. Reson. Med., Vol. 6 (1988), page 164; B. R. Rosen et al, Magn. Reson. Q., Vol. 5 (1989), page 26; C. T. W. Moonen et al, Science, Vol. 250 (1990), page 53; J. W. Belliveau et al, Science, Vol. 254 (1990), page 716) and of local changes in brain oxygenation state (S. Ogawa et al, Magn. Reson. Med., Vol. 14 (1990), page 68; R. Turner et al, Magn. Reson. Med., Vol. 22 (1991), page 159). Most of these studies are carried out with echo-planar MRI methods because of their high intrinsic sensitive for T2*. In principle, conventional methods based on gradient-recalled echoes (A. Haase et al, Magn. Reson., Vol. 67 (1986), page 258; D. Matthaei et al, Lancet, Vol. 2 (1985), page 893; F. W. Wehrli, Magn. Reson. Q., Vol. 6 (1990), page 165) are also T2* sensitive, but the T2* sensitivity generally has to be compromised in order to reach the desired time-resolution. For example, blood volume measurements in the brain based on tracking the passage of a bolus of contrast agent require a time-resolution of the order of 1 s per image due to the short transit time of blood. For 128 phase encode steps, this limits the TR (repetition time) to about 8 ms and TE (echo time) to about 5 ms.
The present invention, hereafter referred to as an "echo-shifted" gradient-recalled echo method, involves methods of magnetic resonance imaging which have enhanced sensitivity to T2* changes, as compared to methods known heretofore.